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PHOENIX -- By many accounts, this was a pivotal week in the Jodi Arias murder trial.

Arias, who has spent 13 days testifying on the stand so far, broke down Thursday, as Prosecutor Juan Martinez grilled her about inconsistencies in her testimony, and how she killed her ex-boyfriend, Travis Alexander.

"The first couple days on cross-examination, [Arias] came across as smug and confident. Over the course of the days, he beat her down with questions, to the point where she was a mess on the stand," crime writer Shanna Hogan told 3TV.

Arias buried her face in her hands as Martinez asked for details on the killing, but Hogan, who is writing a book on the saga, called it an 'act.'

"Part of her breakdown was an act. This is her playing a part for the jury," added Hogan, who called Arias' breakdown, "the key moment" of the case so far.

Arias' story is full of holes, by her own admission. She says she remembers shooting Alexander at his home in Mesa, but cannot remember stabbing him 27 times, or slitting his throat.

The prosecutor showed the jury evidence he says proves Arias rented a car in California, stole a gun from her grandfather, filled several containers of gasoline, turned her phone off, and drove to Mesa specifically to kill Alexander.

"He proved pre-meditation. He asked the hard questions the jury would want to ask, the questions the family would want to ask. This was the week, the week that damned her, and maybe put her on death row," said Hogan, who sat through much of the testimony in court.

Trial resumes, with Arias expected to be back on the stand, Monday morning.